Multiple output charge pump

ABSTRACT

A single mode buck/boost charge pump has multiple outputs and is adapted to power a plurality of separate loads, such as light emitting diodes, in a highly efficient manner. The multiple outputs have different voltages. The output current or voltage of at least one of the multiple outputs is regulated by a feedback circuit. The feedback circuit provides a control signal based on a comparison of a reference voltage with a feedback voltage. The feedback voltage is proportional to an output voltage when the charge pump is configured to regulate the output voltage. Alternately, the feedback voltage is a sense voltage across a sense resistor connected in series with a load when the charge pump is configured to regulate output current provided to the load.

RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/880,528, filed on Jun. 12, 2001, which claims the benefit ofU.S. Provisional Application No. 60/211,167, filed on Jun. 13, 2000, andentitled A Single Mode, Buck/Boost, Regulating Charge Pump, A Method toImprove the Efficiency Thereof, and a System Using the Charge Pump in aCombination LED Current Regulator and Voltage Converter, the entirety ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to the field of voltage convertersand in particular to a charge pump voltage converter.

[0004] 2. Description of the Related Art

[0005] Many electrical devices require power supplied at a stablevoltage different than that provided by a primary power source. In manyapplications, the primary power source is a battery. Often theelectronic devices require voltages that are between 1 and 2 times thevoltage provided by the battery. An additional requirement is that thevoltage provided be relatively stable. A low voltage can result in thepowered devices failing to operate at all or at a reduced performancelevel. Steady overvoltage can reduce the life of the devices orpermanently damage the devices. Spikes or transients in voltage can alsodisrupt device operation and cause damage.

[0006] One difficulty with batteries is that many batteries do notprovide a stable output voltage. The output voltages of many batteriesdecrease as the batteries are used and as the batteries age. Thevoltages can also vary depending on how heavily the batteries areloaded. Certain batteries also vary in output voltage with variations intemperature. Even under conditions where the battery voltage is notvarying, the battery may provide power at a different voltage than thatrequired by user devices.

[0007] Charge pumps are known circuits that effectively transferelectrical charge back and forth between storage components to generatean output voltage different from an input voltage. Charge pumps with a“buck” feature are effectively voltage limiters. If the input voltageexceeds a threshold value, the charge pump “bucks” the overvoltage awayfrom the load. However, in a charge pump circuit, the charge is notsimply shunted to ground or another load as in, for example, zener diodecircuits. A charge pump temporarily stores the charge redirected fromthe load, typically in a capacitive element. This charge stored in thecapacitor is then typically delivered to the load at a later time. Zenerdiodes are effective at clamping voltages above a certain threshold;however, by simply shunting the current away from the load, the currentis typically not available for use. This results in wasted power. Itwill be appreciated that wasting power in a device with limited batterycapacity is preferably avoided.

[0008] In a “boost” operation, a charge pump accumulates charge to beable to provide a greater voltage to the load than is provided by theinput voltage. A charge pump in boost operation typically sequentiallycharges at least one capacitor connected in parallel with the powersource and then selectively interconnects the capacitor(s) in serieswith power source to increase the available voltage for delivery to theload. Typical charge pump circuits double or triple the input voltageminus some switching and other loses. Again, it will be appreciated thatminimizing loses from a limited power source such as a battery isdesirable.

[0009] Charge pump circuits are often used in consumer electronics, suchas PDAs, cell phones, and the like. Thus, it will be appreciated thatsimplicity and low cost are highly desirably. With potential markets inthe millions of units, a reduction in cost of only a few cents can addup to significant savings and increased profits for the manufacturersand sellers. An additional design goal is to reduce size and weight ofthe devices. Reduced size and weight increases the convenience of anappliance to the consumer and increases the marketability of theappliance. Many known charge pump designs employ multiple operatingmodes that increase circuit complexity and cost of the charge pumps.Multiple operating modes also generally lead to voltage transients uponswitching between the multiple modes, which again can damage powereddevices.

[0010] An additional problem with the charge pump circuits is that theconversion efficiency declines very quickly when the output voltage isless than twice the input voltage. The general rule for any charge pumpis that input current will always be twice the output current when thecircuit is in equilibrium. Current is drawn from the battery on everyclock cycle; however, it is only supplied to the load every other clockcycle. Thus, the instantaneous current is the same in the input andoutput sides, but the time average current for the input is twice theoutput. Since efficiency is the ratio of power out divided by power in,and input current is always twice output current, the maximumtheoretical efficiency can be calculated as follows:

Eff=Pout/Pin

Eff=(Iout×Vout)/(Iin×Vin)

Eff=(Iout×Vout)/(2×Iout×Vin)

Eff=(Vout/(2×Vin))×(100%)

Therefore: Eff=100% max when Vout=2 Vin

Eff=50% max when Vout=Vin

Eff=25% max when Vout=½ Vin

[0011] In practical circuits, it is reasonable to expect 10% losses inthe converter because of resistive losses in switching components andjunction drops. The actual predictions made by multiplying thetheoretical predictions above by 90% are 90%, 45% and 22%, respectively.

[0012] One reason for the low efficiency numbers when Vout is <2 Vin isthat the charge current for the transfer capacitor Cx flows from thebattery directly to ground without imparting its full energy on Cx,(i.e., Cx is not charged to the battery's full potential). Thus, thevoltage difference between the available battery potential and thevoltage needed to charge Cx to obtain the desired output voltage isavailable, but is not utilized.

[0013] Many real world battery-powered applications that includemultiple loads with different power requirements and meet the criteriafor using a secondary load output from the charge pump. For example,cellular telephones and handheld computers (PDAs) are typically poweredby single cell Lithium-ion or triple cell NiCad batteries havingterminal voltages that range from 5.6 volts at full charge to 3.0 voltsat cutoff. A common requirement in these products is to provide oneregulated output voltage in the 5-volt to 3.3-volt range and to providea second regulated output voltage in the 2.5-volt 1.5-volt range.

[0014] A very specific application in the cellular phone product area isdriving a combination of white and green LEDs that light a color displayand a keypad. White LEDs are needed to provide good color from a liquidcrystal thin film transistor (TFT) display. These white LEDs typicallyhave forward voltage drops of 3.6V and draw approximately 20 mA each.Therefore. the white LEDs require a buck/boost voltage converter tooperate from the normal 5.6-volt to 3.0-volt battery potential. Anadditional requirement for the white LEDs is that all the LEDs generateapproximately the same light intensity in order to achieve uniformlighting in the display.

[0015] The cell phone also uses a lighted key pad, but this can uselower cost and lower voltage green LEDs. Uniformity of lighting andcolor trueness of the keypad is less of a concern than with the display.Green LEDs operate at 2.0 volts at 10 mA drive levels, thus using lesspower per LED (20 mW) than white LEDs (72 mW). However, because theelectrical requirements of green and white LEDs differ, two separatecircuits are typically required to enable to advantages of using greenand white LEDs.

[0016] In order to maintain a constant and consistent light output,multiple LEDs require a constant current rather than constant voltage.One method of driving LEDs is to use a constant voltage source withcurrent limiting ballast resistors in series with the LEDs to senseand/or control forward current. Multiple LEDs can be driven in parallelor in series. If in series, only one series resistor is required for theLEDs in that branch, however the supply voltage must be high enough tosupport the sum of the forward voltages of the LEDs. Unfortunately, thevoltage required for two or more LEDs is higher than readily achievablewith a switched capacitor charge pump fed by a typical battery.

[0017] When multiple LEDs are driven in parallel, the supply voltageonly needs to be in the 4V range, which is easily achievable with acharge pump operating from a 3-volt battery. In the parallel case, eachLED has its own series resistor to control and balance its current.However, this approach has two weaknesses:

[0018] 1. Current matching among the LEDs is needed to insure equallight output. Individual LEDs will have different forward voltage dropsat equal drive currents. Because of this, the value of a series ballastresistor must be fairly high to control current sharing withoutundertaking the significant time and expense of testing and selectingLEDs for minimal variations in forward voltage. Typically, dropping atleast one-fourth of the forward voltage of the LEDs would be needed tomaintain less than 10% current variation among the multiple LEDs. With aprimary supply voltage of 3.0 volts providing power to a charge pumppowering white LEDs with 3.6-volt forward voltage drops, 0.9 volts wouldtypically be needed across the series resistor to achieve less than 10%current variation. This would result in a 20% loss because one-fifth ofthe total supply voltage is used in the ballast resistor and energy islost to resistive heating rather being used for the desired lightproduction.

[0019] 2. The product would be burdened with the extra space and cost ofthe series resistors.

[0020] Thus, from the foregoing it will be appreciated that there is aneed for an efficient charge pump that provides both buck and boostoperations and that provides an output voltage that is regulated toprovide a stable output voltage even in the presence of variations in aninput voltage. A need also exists for a regulating charge pump of simpledesign that avoids the cost and complexity of multiple operating modes.A need also exists for a charge pump that avoids switching betweenmultiple operation modes and that minimizes switching transients.Furthermore, a need exists for a buck/boost capable charge pump that canprovide regulated outputs at different voltage levels with a singlecircuit. Advantageously, such a multiple output regulating charge pumpoperates with improved efficiency. Moreover, a need exists for a singlecircuit that provides multiple voltage regulated outputs and that alsoregulates the current in multiple branches of at least one of theoutputs so as to facilitate powering LEDs in a highly efficient andbalanced manner.

SUMMARY OF THE INVENTION

[0021] One aspect of the present invention solves these and otherproblems by providing a single mode buck/boost charge pump that providesa regulated constant output voltage between zero and twice an inputvoltage without changing control modes or interrupting circuit operationwhen the input voltage falls below or rises above a set output voltage.In one embodiment, a single mode buck/boost charge pump is adapted topower a plurality of separate loads in a highly efficient manner. Inanother embodiment, a single mode buck/boost charge pump is acombination current regulator and multiple output regulating charge pumpadapted for driving LEDs in a highly efficient and balanced manner.

[0022] In one aspect of the present invention, a regulating charge pumpprovides buck and boost operation in a single operating mode wherein thecharge pump provides an output voltage that is a multiple of anindependent reference voltage and wherein a charge storage component ischarged by a regulated variable current supply. In one embodiment, thevariable current supply is regulated with respect to the referencevoltage and the output voltage and the charge storage component isalternately charged by the regulated variable current supply andconnected in series with the output. In certain embodiments, the chargestorage component is inhibited from being charged when connected inseries with the output.

[0023] In certain embodiments, the reference voltage is a fixed voltage,and in alternative embodiments, the reference voltage is selectable fromamong a plurality of voltage values.

[0024] In another aspect of the present invention, a regulating chargepump receives a supply voltage and provides a regulated output voltage.The charge pump comprises a charge storage component, a plurality ofswitches interconnecting the charge storage component and the supplyvoltage, a switch timing control that regulates the states of theplurality of switches, a reference voltage source, an error amplifierconnected to the reference voltage source and the regulated output, anda variable current supply that receives control signals from the erroramplifier and provides regulated current to the charge storage componentin response to the output voltage, wherein the output voltage isregulated with respect to the reference voltage source. In particularembodiments, the switch timing control alternately connects the chargestorage component to the variable current supply and in series with theregulated output. In certain embodiments thereof, the switch timingcontrol inhibits connecting the charge storage component to the variablecurrent source and the output simultaneously. The switch timing controloperates in a periodic fashion.

[0025] In certain embodiments, the reference voltage is a fixed voltage.In alternative embodiments, the reference voltage is selectable fromamong a plurality of voltage values. In other embodiments, the erroramplifier comprises a feedback network and in certain embodimentsthereof, the feedback network comprises a voltage divider connected tothe regulated output.

[0026] In a further aspect of the present invention, a method provides astable output voltage. The method comprises providing an input voltageand providing a reference voltage. The method sequentially charges acharge storage component via a regulated variable current source andconnects the charge storage component in series with the input voltageso as to generate the output voltage. The method monitors the outputvoltage and regulates the charging of the charge storage component suchthat the output voltage is a multiple of the reference voltage.

[0027] In one embodiment, the present invention is useful in charge pumpapplications where a supply voltage, Vin, is higher than a minimumsupply voltage needed to provide the output voltage Vout. Thus, thecharge component is not charged to a maximum value that it can reach.The difference between the minimum supply voltage and the maximumvoltage on the charge storage component is used to generate a secondvoltage output from the circuit. The second voltage output is suppliedto a second, separate load. In this aspect, the present invention isable to supply different multiple regulated outputs from a single inputvoltage. In certain embodiments, the input voltage is lower than oneoutput voltage and higher than the other output voltage.

[0028] For example, at a minimum battery voltage of 3.0V, white LEDsrequire a 0.6-volt boost, plus about 200 mV to implement a constantcurrent driver. Thus, the minimum output voltage provided to white LEDsmust be about 3.9 volts to account for other circuit losses. The totalboost required from a charge pump is then 3.9−3.0=0.9 volts. Since theminimum battery voltage is 3.0 volts and the 0.9-volt boost must appearacross the charge transfer component while it is being charged, thedifference of 2.1 volts (3.0−0.9) is available to drive the second load.It is common to use four green LEDs operating at 10 mA to light thekeypad. The remaining 2.1 volts is adequate to do this with 100 mV leftover for circuit losses. The total current required by two white LEDs isapproximately the same as required by the four green LEDs. This isadvantageous because virtually all of the unused energy from the chargepump can be diverted to the green LEDs. In addition, since both thewhite LEDs and the green LEDs are typically turned on at the same time,it is advantageous to share the same charge pump circuit.

[0029] In one aspect of the present invention, a charge pump receives asupply voltage wherein the charge pump provides multiple regulatedoutputs. In one particular embodiment, the multiple regulated outputsare at different voltages, and at least one of the multiple outputs isregulated at a voltage different than the supply voltage. In certainembodiments, the outputs are regulated independently with respect toinput voltage.

[0030] In another aspect of the present invention, at least one of theoutputs is regulated with respect to a parameter of a load connected tothe at least one output. In one particular embodiment, the parameter ofthe load corresponds to an output node of the load. In anotherembodiment, regulating the at least one output with respect to theparameter of the load automatically compensates the at least one outputfor variations in the parameter of the load. In this embodiment, thevariations in the parameter of the load include variations due totemperature change.

[0031] In a further aspect of the present invention, a multiple outputregulating charge pump receives a supply voltage. The charge pumpcomprises a charge storage component, a plurality of switchesinterconnecting the charge storage component and the supply voltage, aswitch timing control that regulates the state of the plurality ofswitches, a reference voltage source, and a feedback circuit thatprovides regulated current to the charge storage component in responseto the output voltage, wherein the output voltage is regulated withrespect to the reference voltage source. In certain embodiments, themultiple outputs provide regulated voltages to at least a first load anda second load. In a particular embodiment, the output voltage is furtherregulated with respect to at least one of the first load and the secondload. In an embodiment thereof, the output voltage is regulated withrespect to an output node of at least one of the first load and thesecond load.

[0032] In yet another aspect of the present invention, the switch timingcontrol operates the switches so as to alternately charge and dischargethe charge storage component. In one embodiment, charging the chargestorage component comprises connecting the charge storage component inseries with the supply voltage and the second load, and discharging thecharge storage component comprises connecting the charge storagecomponent in series with the supply voltage and the first load. In acertain embodiment, current is provided to the first load as the chargestorage component is discharged and is provided to the second load asthe charge storage component is charged. In another embodiment, theswitch timing control operates the switches so as to inhibit having thecharge storage component connected in series with the supply voltage andboth the first and the second loads simultaneously.

[0033] In particular embodiments of the invention, the feedback circuitcomprises a variable current source and an error amplifier and thevoltage reference provides a fixed reference voltage. In a furtherembodiment, the reference voltage is selectable among a plurality ofreference voltage values.

[0034] In one embodiment, a multiple output regulated charge pump iscombined with constant current sinks for multiple white LEDs to providean LED driver and a load current regulator with higher efficiency. Thisalso results in a lower component count. In addition, a greater accuracycan be obtained for cell phone and PDA applications that must operatefrom batteries having voltages that range from 3.0 volts to 5.6 volts.The device is scaleable to different quantities of LEDs by simply addinga current sink for each additional white LED in the application. Theload current regulator is capable of maintaining less than 10% currentvariation among the white LEDs with only a 300 mV overhead andeliminates the need for ballast resistors in the load.

[0035] In one aspect of the present invention, a multiple outputregulating charge pump receives a supply voltage and provides at least afirst regulated output and a second regulated output. The firstregulated output has a voltage that can be regulated at a leveldifferent than the voltage of the supply, and the current provided to aload by the first output voltage is actively current regulated. Incertain embodiments, the first output is voltage regulated with respectto an output node of the load connected to the first output, therebyautomatically compensating for variations in load characteristics.

[0036] One aspect of the present invention is a charge pump with acharge storage component and a plurality of switches connected to thecharge storage component under control of a switch timing controlcircuit. The switch timing control circuit controls the switches tosequentially connect the charge storage component to the supply inseries with the first output and then in series with the second output.The charge storage component is alternately charged when connected inseries with the second output and discharged when connected in serieswith the first output so as to provide the first regulated outputvoltage. The switch timing control operates to prevent the chargestorage component being connected to both the first and the secondoutputs simultaneously. In certain aspects of the invention, the switchtiming control receives timing signals from an oscillator such that theswitch timing control circuit operates to open and close the switches ina periodic fashion.

[0037] In another aspect of the present invention, a current is suppliedto a load connected to the second output when the charge storagecomponent is being charged and at least the first output is voltage andcurrent regulated so as to provide substantially equal currents tomultiple branches of the load connected to the first output.

[0038] Another aspect of the invention is a load current regulator thatregulates the current provided to the load connected to the firstoutput. In particular, the load current regulator regulates the currentamong the multiple branches of the load connected to the first outputsuch that the current in each of the branches of the load issubstantially equal.

[0039] In certain embodiments, the load current regulator comprises aplurality of transistors arranged in a current mirror configuration andthe load connected to the at least first output comprises a lightemitting diode.

[0040] A further aspect of the present invention is a regulating chargepump that receives a supply voltage and that provides regulated voltagesto at least two loads. The charge pump comprises a charge storagecomponent, a variable current source, an error amplifier that receivesfeedback from at least one of the loads and provides control signals tothe variable current source, and a plurality of switches thatinterconnect the supply, the charge storage component, the variablecurrent source, the error amplifier, and the at least two loads. Aswitch timing control circuit controls the operation of the switchessuch that the variable current source can supply current to the chargestorage component and directly to at least one of the loads. A loadcurrent regulator is connected to at least one of the loads such thatcurrents within multiple branches of the load are actively balanced.

[0041] In certain embodiments, the error amplifier receives feedbackfrom an output node of the at least one load. The switch timing controlcircuit operates the switches such that the charge pump alternatelyprovides regulated voltage to a first load as the charge storagecomponent discharges and provides regulated voltage to a second load asthe charge storage component is charged.

[0042] In certain embodiments in accordance with the foregoing aspectsof the present invention, the charge pump includes a switch timingcontrol circuit that operates the switches in a periodic manner. Theswitch timing control circuit prevents all the switches from beingturned on at the same time. The load current regulator comprises aplurality of transistors arranged in a current mirror configuration.

[0043] The foregoing aspects of the present invention will become morefully apparent from the following description taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Embodiments of the present invention will be described in detailbelow in connection with the accompanying drawings, in which:

[0045]FIG. 1 is a circuit diagram of a typical prior art unregulatedswitched capacitor voltage doubler;

[0046]FIG. 2 is an equivalent circuit diagram of the circuit of FIG. 1during a charge half-cycle;

[0047]FIG. 3 is an equivalent circuit diagram of the circuit of FIG. 1during a discharge half-cycle;

[0048]FIG. 4 is a circuit diagram of one embodiment of a regulatedbuck/boost charge pump of the present invention;

[0049]FIG. 5 is an equivalent circuit diagram of the regulated chargepump of FIG. 4 during a charge half-cycle;

[0050]FIG. 6 is an equivalent circuit diagram of the regulated chargepump of FIG. 4 during a discharge half-cycle;

[0051]FIG. 7 is a timing diagram of one embodiment of a switch timingcontrol;

[0052]FIG. 8 is a circuit diagram of one embodiment of a switch timingcontrol;

[0053]FIG. 9 is a circuit diagram of one embodiment of a multiple outputcharge pump;

[0054]FIG. 10 is an equivalent circuit of the multiple output chargepump of FIG. 9 during a charge half-cycle;

[0055]FIG. 11 is an equivalent circuit diagram of the multiple outputcharge pump of FIG. 9 during a discharge half-cycle;

[0056]FIG. 12 is a circuit diagram of an alternate embodiment of amultiple output charge pump;

[0057]FIG. 13 is a circuit diagram of a charge pump with load currentregulation;

[0058]FIG. 14 is a circuit diagram of the charge pump with load currentregulation of FIG. 13 during a charge half-cycle, providing power to asecond load;

[0059]FIG. 15 is a circuit diagram of the charge pump with load currentregulation of FIG. 15 during a discharge half-cycle providing regulatedvoltage and current to multiple branches of a first load; and

[0060]FIG. 16 is a detailed circuit diagram of the charge pump with loadcurrent regulation of FIG. 13.

DETAILED DESCRIPTION OF THE INVENTION

[0061] Reference will now be made to the drawings wherein like numeralsrefer to like parts throughout. FIGS. 1-3 illustrate a typical prior artcharge pump voltage doubler circuit. The charge pump circuit includesfour semiconductor switches, S1-S4, represented in the drawings assingle-pole, single-throw (SPST) switches. The four switches arecontrolled to alternately connect a charge transfer capacitor, C_(x), inparallel with a source supply (e.g., a battery) during a charge halfcycle illustrated in FIG. 2, and to then connect the charge transfercapacitor, C_(x), in series with the supply and a load during adischarge half cycle illustrated in FIG. 3. A load resistor, R_(load),is connected in parallel with an output capacitor, C_(out). The outputcapacitor stores energy transferred from the transfer capacitor, C_(x),during the discharge half cycle in FIG. 3 and transfers the energy tothe load during the charge half cycle in FIG. 2. The odd numberedswitches, S1 and S3, are closed during the charge half cycle (FIG. 2),and the even numbered, S2 and S4, are closed during the discharge halfcycle (FIG. 3). A square wave oscillator generates a timing signal to aswitch timing control circuit. The switch timing control circuitgenerates control signals to the four switches that determine when theswitches are opened and closed. The switch timing control circuit turnsoff the switches S1 and S3 before turning on the switches S2 and S4.Similarly, the switch timing control circuit turns off the switches S2and S4 before turning on the switches S1 and S3. This “dead time”between the opening of one pair of switches and the closing of the otherpair of switches prevents both sets of switches from being on at thesame time.

[0062] In the following discussion, the following relationships betweenthe elements in FIGS. 1-3 are assumed:

[0063] C_(x) charge time=C_(x) discharge time

[0064] C_(x) charge current>C_(x) discharge current during start up.

[0065] C_(x) charge current=C_(x) discharge current during steady stateoperation.

[0066] Voltage across C_(x)=Voltage across V_(in)

[0067] V_(out) 2×V_(in)

[0068] In FIG. 2, when S1 and S3 are closed, the semiconductor switcheshave on resistances of approximately 5 ohms and are represented byresistors R_(S1) and R_(S2), respectively. Using this representation, itcan be seen that:

C_(x) charge current=[V_(IN)/(R_(S1)+R_(S3))]×[e ^(−t/RC)],

where RC=(R_(S1)+R_(S3))(C_(x))

[0069] In FIG. 3, S2 and S4 are closed and are represented by 5-ohmresistors, R_(S2) and R_(S4), respectively. Thus, it can be seen that:

C_(x) discharge current=[(VIN−VOUT)/(R_(S2)+R_(S4))]×[e ^(−t/RC)],

where RC=(R_(S2)+R_(S4))×(C_(x)),

and where C_(out)>>C_(x).

[0070] In the configuration illustrated in FIGS. 1-3, the outputvoltage, V_(out), is a function of the input voltage, V_(in), and isdetermined both by circuit component values and by V_(in). Thus, theoutput voltage will vary with the input voltage. As previouslymentioned, variations in the output voltage of a charge pump can havedeleterious effects on other circuits and components receiving powerfrom the charge pump.

[0071]FIG. 4 illustrates one embodiment of a regulating charge pump 100in accordance with the present invention. The regulating charge pump 100receives electrical power from a primary power source 102 and provides aregulated output in a manner that will be described in greater detailbelow. In certain embodiments, the power source 102 comprisessingle-cell Lithium-ion or 3-cell Nickel-Cadmium (NiCad) batteries oftypes well known in the art. The power source 102, in one embodiment,provides input power on a terminal 103 at a voltage V_(in) that variesfrom approximately 5.6V at full charge to approximately 3.0V at cutoff.

[0072] The regulating charge pump 100 also comprises semiconductorswitches (S1) 104, (S2) 106, (S3) 110 and (S4) 112. The switches 104 and106 have respective firs terminals that are connected to the powersource 102. A second terminal of the switch 104 is connected to a firstterminal of the switch 112. A second terminal of the switch 112 isconnected to an output terminal 142 that provides an output voltage,V_(OUT). The second terminal of the switch 112 is also connected to afirst terminal of a resistor 132. A second terminal of the switch 106 isconnected to a first terminal of the switch 110. A second terminal ofthe switch 110 is connected to a variable current source 122, discussedbelow.

[0073] The regulating charge pump 100 also comprises a charge storagedevice C_(x) 114 that is connected between a node V_(CX1) and a nodeV_(CX2). The node V_(CX1) is connected to the second terminal of theswitch 104 and to the first terminal of the switch 112. The node V_(CX2)is connected to the second terminal of the switch 106 and to the firstterminal of the switch 104. In one embodiment, the charge storage deviceC_(x) 114 comprises a non-polarized capacitor of 1 μF of a type wellknown in the art. As discussed above in connection with FIGS. 1-3, thecharge storage device C_(x) 114 of FIG. 4 temporarily stores anelectrical charge to enable the regulating charge pump 100 to deliver anoutput V_(out) on the node 142 in a manner that will be described ingreater detail below.

[0074] The regulating charge pump 100 also comprises a switch timingcontrol circuit 116. The switch timing control circuit 116 generatestiming signals T1 172 and T2 174 (illustrated in FIGS. 7 and 8) tocontrol the switching of the switches 104, 106, 110, and 112 in a mannerthat will be described in greater detail below. In a preferredembodiment described herein, the switch timing control circuit 116controls the switches 104 and 110 to operate in concert as a first pairof switches and controls the switches 106 and 112 to operate in concertas a second pair of switches. In particular, the switches 104 and 110are closed and opened together, and the switches 106 and 112 are closedand opened together. As discussed above, the complementary closing andopening of the switches 104 and 110 with respect to the switches 106 and112 is regulated by the switch timing control circuit 116 such that theswitches 104 and 110 open completely before the switches 106 and 112 areclosed and such that the switches 106 and 112 open completely before theswitches 104 and 110 are closed to thereby prevent both pairs ofswitches from being closed simultaneously.

[0075] The regulating charge pump 100 also comprises a conventionalsquarewave oscillator 120. In the preferred embodiment, the square-waveoscillator 120 generates a square-wave signal F_In 170 (FIG. 7) that hasa frequency of approximately 500 kHz. The square-wave oscillator 120provides a timing clock to the switch timing control circuit 116. Theswitch timing control circuit 116 generates the T1 control signal 172and the T2 control signal 174 in synchronism with the timing clock toprovide the timing control signals for the opening and closing of theswitch pairs 104 and 110 and 106 and 112.

[0076] As shown in FIG. 7 for the preferred embodiment, the T1 signal172 is substantially in phase with the F_In signal 170; however, therising edge of the T1 signal 172 lags the rising edge of the F_In signal170 by approximately 60 nanoseconds. The falling edge of the T1 signal172 occurs substantially synchronously with the falling edge of the F_Insignal 170. The T2 signal 174 is substantially 180° out of phase withthe F_In signal 170 such that the rising edge of the F_In signal 170occurs synchronously with the falling edge of the T2 signal 174. Therising edge of the T2 signal 174 lags the falling edge of the F_Insignal 170 by approximately 60 nanoseconds. Thus, both the T1 signal 172and the T2 signal 174 are high for alternating 940-nanosecond periods ata frequency of approximately 500 kHz with 60-nanosecond null periodsinterposed between the active periods of the T1 signal 172 and the T2signal 174. Thus, the switch pairs 104, 110 and 106, 112 are closed foralternating 940-nanosecond periods with 60 nanoseconds of dead timebetween each closed period.

[0077]FIG. 8 is a circuit diagram of one embodiment of the switch timingcontrol circuit 116. The switch timing control circuit 116 receives theF_In signal 170 on an input terminal, as previously described. A 50resistor R7 176 is connected between the input terminal and circuitground 130. The F_In signal 170 is also coupled to the input of aninverter 180. The output of the inverter 180 is connected to both inputsof an AND gate 182 and to a first input of an AND gate 184. The outputof the AND gate 182 is connected to a second input of the AND gate 184with a delay circuit 194 interposed therebetween. The delay circuit 194of this embodiment comprises a resistor R9 connected between the outputof the AND gate 182 and the second input of the AND gate 184 and acapacitor C3 connected between the second input of the AND gate 184 andthe circuit ground. The component values of the delay circuit 194 areselected to provide a 60-nanosecond delay between the output of theinverter 180 and the second input of the AND gate 184. The output of theAND gate 184 generates the T2 signal 174. Thus, a rising edge of theF_In signal 170 causes an immediate falling edge of the T2 signal 174. Afalling edge of the F_In signal 170 causes a rising edge of the T2signal 174 after a delay of approximately 60 nanoseconds.

[0078] The switch timing control circuit 116 of this embodiment alsocomprises an AND gate 186 having both inputs connected directly to theinput terminal to receive the F_In signal 170. The F_In signal 170 isalso connected to a first input of an AND gate 190. A delay circuit 192,comprising a resistor R8 and a capacitor C2, is also interposed betweenthe output of the AND gate 186 and the second input of the AND gate 190in a comparable manner to that previously described with respect to thedelay circuit 194. The output of the AND gate 190 generates the T1signal 172. A falling edge of the F_In signal 170 causes an immediatefalling edge of the T1 signal 172 on the output of the AND gate 190. Arising edge of the F_In signal 170 causes a rising edge of the T1 signal172 after a delay of approximately 60 nanoseconds through the delaycircuit 194.

[0079] In the illustrated embodiment of the switch timing controlcircuit 116, the inverter 180 is advantageously a type 74ACT11240integrated circuit, and each AND gate 182, 184, 186, 190 isadvantageously a type 74ACT08 integrated circuit. In this embodiment,the delay circuits 192, 194 each comprise a 200Ω resistor and a 200 pFcapacitor. It will be appreciated that other component values and typescan be incorporated for alternative embodiments without detracting fromthe spirit of the present invention as described in this embodiment.

[0080] As further illustrated in FIG. 4, the regulating charge pump 100also comprises a variable current source 122. The variable currentsource 122 is connected to the second terminal of the switch 110 toselectively provide a regulated current IS1 156 to the charge storagecomponent, C_(x), 114 in a manner that will be described in greaterdetail below. The variable current source 122 in this embodiment iscapable of sourcing or sinking the regulated current IS1 156 at amagnitude up to approximately 100 mA.

[0081] The regulating charge pump 100 also comprises an error amplifier124. The amplifier 124 is connected to the variable current source 122to regulate the current supplied by the variable current source 122 tothe charge storage component 114 via switch 110 in response to afeedback signal from the output voltage generated by the regulatingcharge pump 100. In this embodiment, the amplifier 124 is an operationalamplifier (OpAmp) of a type well known in the art.

[0082] A voltage reference 126 is connected between the non-invertinginput of the amplifier 124 and the circuit ground 130. In thisembodiment, the voltage reference 126 provides a fixed 1.0 volt DCsignal. In alternative embodiments, the voltage reference 126 provides avariable signal. For example, the voltage reference 126 isadvantageously selectable among a plurality of fixed values.

[0083] The regulating charge pump 100 also comprises a resistor (R1) 132and a resistor (R2) 134. As discussed above, the first terminal of theresistor 132 is connected to the second terminal of the switch 112. Asecond terminal of the resistor 132 is connected to the inverting inputof the amplifier 124 and also to a first terminal of the resistor 134.The second terminal of the resistor 134 is connected to the circuitground 130. In this embodiment, the resistor 132 has a value ofapproximately 230 k and the resistor 134 has a value of approximately100 k.

[0084] The resistors 132 and 134 form a voltage divider 136 between thesecond terminal of the switch 112 and the circuit ground 130, whereinthe common connection between the two resistors is a voltage divisionnode that is connected to the inverting input of the amplifier 124. Theamplifier 124, the voltage reference 126, and the voltage divider 136form a feedback circuit 140. The feedback circuit 140 provides controlinputs to the variable current source 122 in response to the voltage atthe second terminal of the switch 112.

[0085] The voltage at the second terminal of the switch 112 is also theoutput voltage, V_(OUT) on the node 142. The output voltage V_(OUT) onthe node 142 is provided to a load 400. In this embodiment, the load 400comprises a resistive component in parallel with a capacitive component.The resistive component of the load has a resistance of approximately44, and the capacitive component of the load has a capacitance ofapproximately 100 μF.

[0086] With the component values previously described for thisembodiment, a V_(OUT) of 3.3 volts on the node 142 generates a voltageat the voltage dividing node of the voltage divider 136 and thus at theinverting input of the amplifier 124 of approximately3.3×(100/(100+230)) volts=1 volt, which is the same value of the voltagereference 126 as provided to the non-inverting input of the amplifier124. Thus, it will be appreciated that a V_(OUT) of 3.3 volts on theterminal 142 will generate a minimal feedback signal from the feedbackcircuit 140 and thus induce a steady state current from the variablecurrent source 122. When V_(OUT) on the terminal 142 is not equal to 3.3volts, the feedback circuit 140 will source or sink a regulated currentIS1 to attempt to return the voltage V_(OUT) on the terminal 142 to 3.3volts in a manner that will be described in greater detail below.

[0087] The regulated charge pump 100 may be considered to include asimulated variable battery (C_(x)) that can assume any DC voltage from+V_(IN) to −V_(IN). The simulated battery can be alternately connectedin parallel or in series with the power source 102. When in series, thesimulated battery supplies current to the load along with the powersource 102. When in parallel, the simulated battery is recharged. Theabsolute value and polarity of the DC voltage across C_(x) is determinedby the magnitudes of the input and output voltages so that the followingequations are met:

V_(OUT)=V_(IN)+V_(CX)

V_(CX)=V_(OUT)−V_(IN)

[0088] In one embodiment, with V_(OUT)=3.3 volts and V_(IN)=3.0 volts,then V_(Cx)=+0.3 volts (i.e., V_(Cx1)=V_(Cx2)+0.3 volts).

[0089] If V_(OUT)=3.3 volts and V_(IN)=6.0 volts, then V_(Cx)=−2.7 volts(i.e., V_(Cx1)=V_(Cx2)−2.7 volts).

[0090] The dynamics of this simulated battery voltage are defined by thefollowing equations:

Q=I×T=CV

V=I×T/C

[0091] where Q is the charge in Coulombs, I is current in amperes, T istime in seconds, C is the value of C_(x) in Farads, and V is the voltageacross C_(x). If the incremental charge and discharge currents in C_(x)are relatively small and if C_(x) is relatively large, the incrementalor ripple voltage on C_(x) will be small. This condition makes thesimulated battery look very much like an actual battery.

[0092] Under steady-state operation, where the average values of V_(in),V_(out) and current in the load do not change, the charging current toC_(x) must equal its discharging current in order to maintain a constantDC voltage across C_(x). In this simulated battery, if the averagecharge current over many pump cycles exceeds the discharge current, apositive voltage (V_(Cx1)>V_(Cx2)) will develop across C_(x). On theother hand, if average discharge current is greater, a negative voltageresults (V_(Cx1)<V_(Cx2)). The feedback circuit 140, as shown in FIG. 4,forces an imbalance of current in the charge storage component, C_(x),114 to adjust its steady-state voltage whenever input voltage or loadcurrent changes.

[0093] Also, since the charge current in C_(x) has a maximum valuedetermined by design, and since I_(OUT) cannot exceed I_(IN) in thistopology (under steady-state conditions), the output is automaticallyshort circuit current limited.

[0094]FIG. 5 is an equivalent circuit diagram of one embodiment of theregulating charge pump 100 during start-up conditions. For illustrationpurposes, the initial conditions are assumed to be:

[0095] V_(IN)=V_(OUT)=V_(Cx)=0 volts

[0096] C_(out)=100 μF

[0097] Cx=1 μF

[0098] Fosc=500 kHz

[0099] V_(out) is set to regulate to 3.3 volts into a 44-ohm load.

[0100] IS1 100 mA (maximum).

[0101] Resistance of each switch 104, 106, 110, and 112=5 ohms

[0102] At power on in this embodiment, V_(IN)=6.0 V. When the oscillator120 starts, the arbitrary assumption will be made that the odd switchpair 104 and 110 will close first as shown in FIG. 5. This places thecharge storage component C_(x) in series with the power source 102 andthe variable current source 122. Thus, a direct current will be providedby the power source 102 to the charge storage component C_(x). Thiscurrent will flow to cause the charge storage component C_(x) to gain asmall positive voltage. Since V_(OUT)=0 volts at startup, the voltage atthe voltage division node 136 of the feedback circuit 140 is also 0volts. Thus, the feedback loop 140 is unsatisfied, and the output of thevariable current source 122 will seek its maximum value, which in thisembodiment is approximately 100 mA. The circuit values will be definedby the equation:

ΔVCx₁=I×tl C which in this embodiment will give values of

ΔVCx₁=100 mA×1 μs/1 μF=+100 mV

[0103]FIG. 6 illustrates a subsequent clock cycle, wherein the chargestorage component C_(x) 114 is connected in series with the power source102 and the load 400 via the closed switch pair 106 and 112. Only theswitch 106 and the switch 112 on resistances (approximately 5 Ω each inthis embodiment) and the load 400 impedance limit discharge current. Theimpedance of the load 400 is negligible under transient conditionsbecause of the relatively high capacitance (100 μF) of C_(OUT). Thecircuit values will be defined by the equations:

ΔVCx₂ =i×t/C,i=V/R×e ^(−t/rc)

ΔVCx₂=((V_(IN)+V_(Cx)−V_(OUT))/2 R_(switch))×(e ^(−t/rc))×(t/C)

[0104] In this embodiment, the corresponding component values willproduce:Δ  VC_(X₂) ≈ ((6 + 0.1 − 0)/10  Ω) × ^(−1µ  S/10  Ω × 1µ  F  )(1µ  S/1µ  F)   ≈ 0.61  volts × 0.95 ≈ 0.580  volts

[0105] Since discharge current in the charge storage component C_(x) 114during the second half cycle (FIG. 6) flows in the opposite direction tothe charge current in the first half cycle (FIG. 5), the voltagedeveloped across the charge storage component C_(x) 114 in the secondhalf cycle is negative with respect to the first half cycle. Therefore,the new value for V_(Cx) is:

V_(Cx)(new)=V_(Cx1)+V_(Cx2)=+0.1−0.580=−0.480 volts

[0106] In subsequent cycles V_(out) on the terminal 142 will riseexponentially toward 3.3 volts while V_(Cx) charges to −2.7 volts DC.When equilibrium is reached, V_(OUT) will be approximately 3.3V, V_(IN)will be approximately 6 volts and V_(Cx) will be approximately −2.7V.The current supplied to the load 400 under steady-state conditions is3.3 volts/44 Ω=75 mA. The charge and discharge currents for the chargestorage component C_(x) 114 are also 75 mA average (150 mA peak), andthe current I_(IN) delivered by the power source 102 is 150 mA average.The peak-to-peak ripple voltage across V_(Cx), assuming an equivalentseries resistance (ESR) of C_(x) is negligible, is 75 mA×1 μS/1 μF=75mV.

[0107] From an efficiency viewpoint, the foregoing example is nearly aworst case since both I_(IN) and V_(IN) are larger than I_(OUT) andV_(OUT). In this example:Eff = POUT/PIN = 3.3 × 0.075/6 × 0.150   = 27.5%, excluding  FET  resistive  losses.

[0108] A similar example can be made for the case where V_(IN) is 3.0V.In this case, C_(x) will also initially charge in a negative direction,but will become zero when V_(OUT) reaches V_(IN), and will finallychange to +0.3V.

[0109]FIG. 9 is a circuit diagram of one embodiment of a multiple outputregulating charge pump 900 (e.g., a dual output charge pump). In oneembodiment, the dual output charge pump 900 is the charge pump shown inFIG. 4 with a second load 152 interposed between the variable currentsource 122 and circuit ground 130. The dual output charge pump 900receives electrical power from a primary power source 102. In thisembodiment, the charge pump 900 provides a first regulated outputV_(OUT1) on the terminal 142 and provides a second regulated outputV_(OUT2) on a terminal 144 in a manner that will be described in greaterdetail below.

[0110] In the embodiment of FIG. 9, V_(OUT1) on the terminal 142 isregulated at approximately 3.9 volts. V_(OUT1) is provided to a firstload 146. The first load 146 advantageously comprises a capacitivecomponent of approximately 10 μF in parallel with a plurality of whitelight emitting diodes (LEDs) 150, with each LED 150 in series with arespective resistor (R3) 162 and (R4) 164.

[0111] The second output voltage V_(OUT2) on the terminal 144 isprovided to a second load 152. In this embodiment, V_(OUT2) is regulatedto provide approximately 40 mA of current to the second load 152. In theembodiment of FIG. 9, V_(OUT2) is the voltage present at the sink poleof the variable current source 122. The second load 152 comprises aplurality of green LEDs 154 connected in parallel between the terminal144 and circuit ground 130 so that the voltage V_(OUT2) appears acrosseach green LED.

[0112] In the embodiment of FIG. 9, the second load 152 is interposedbetween the variable current source 122 and circuit ground 130. Theregulated current 156 flowing from the variable current source 122 isprovided to the second load 152 at a voltage determined by thedifference between the voltage V_(IN) developed by the power source 102and the steady-state charge on the charge storage component 114.

[0113] As discussed above in connection with the charge pump 100 in FIG.5, the regulated charge pump 900 in FIG. 9 may also be considered asincluding a simulated variable battery (C_(x)) that can assume any DCvoltage from +V_(IN) to −V_(IN). The simulated battery can bealternately connected in series with the power source 102 and the firstload 146 or with the second load 152. When in series with the first load146, it supplies current to the first load 146 along with the powersource 102. When in series with the second load 152, it is recharged.The absolute value and polarity of DC voltage across C_(x) is determinedby the magnitudes of the input and output voltages so that the followingequations are met:

V_(OUT1)=V_(IN)+V_(CX)

V_(CX)=V_(OUT1)−V_(IN)

[0114] In one embodiment, with V_(OUT)=3.9 volts and V_(IN)=3.0 volts,then V_(Cx)=+0.9 volts (i.e., V_(Cx1)=V_(Cx2)+0.9 volts).

[0115] If V_(OUT)=3.9 volts and V_(IN)=5.6 volts, then V_(Cx)=−1.7 volts(i.e., V_(Cx1)=V_(CX2)−1.7 volts).

[0116]FIG. 10 is an equivalent circuit of the dual output charge pump900 of FIG. 9 during a charge half-cycle, wherein current is supplied tothe second load 152. In this embodiment, V_(IN)=3.0 volts, and thearbitrary assumption is made that the odd switches 104 and 110 areclosed. This places the charge storage component C_(x) 114 in serieswith the power source 102, the variable current source 122, and thesecond load 152. To maintain V_(OUT1) on the terminal 142 at 3.9 voltswith V_(IN) on the terminal 103 at 3.0 volts, a voltage of 0.9 volts isrequired across the charge storage component 114. The difference of 2.1volts is available at the V_(OUT2) terminal 144. Thus, a regulateddirect current 156 is provided by the power source 102 to the chargestorage component C_(x) 114 through the variable current source 122 andto the second load 152 at 2.1 volts.

[0117] In the embodiment of FIG. 10, each of the four green LEDs 154draws 10 mA of current thus requiring a total regulated current (IS 156)of 40 mA. This current also causes the voltage across the charge storagecomponent C_(x) 114 to increase by 0.9 volts. The output voltageV_(OUT2) available at the terminal 144 has a magnitude of 2.1 volts,which is within the optimal range to power the green LEDs 154.

[0118]FIG. 11 is an equivalent circuit diagram of the dual output chargepump 900 of FIG. 9 during a discharge half-cycle, wherein the chargestorage component C_(x) 114 is connected in series with the power source102 and the first load 146 via the closed switch pair 106 and 112. Inthis condition, the power source 102 provides current through the chargestorage component 114, which adds 0.9V to V_(IN) and provides the totalvoltage as the output voltage V_(OUT1) to the first load 146 via theterminal 142. In the embodiment of FIG. 11, each white LED 150 draws 20mA for a total regulated current of 40 mA from the terminal 142.

[0119] The embodiment of the multiple output regulated charge pump 900described herein is particularly advantageous because the currentsrequired for operation of the first load 146 and the second load 152 aresubstantially identical. Also, in the application of cell phones, PDAs,and the like, both the white LEDs 150 of the first load 146 and thegreen LEDs 154 of the second load 152 are normally on at the same time.It will be appreciated that to a user of the device, sequentiallyturning on the white 150 and green LEDs 154 for 1 μs periods at 500 kHzwill appear to be a seamless, continuous operation.

[0120] The overall system level efficiency, defined here as the powerdissipated in the LEDs 150, 154 neglecting loses in the ballastresistors 162, 164 and neglecting switch loses at the minimum inputvoltage level V_(IN) of 3.0 volts from the power source 102 is definedby:

Eff=Pout/Pin=(Pwhite+Pgreen)/Pin

Pout=3.6V×40 mA+2.0V×40 mA=224 mW

Pin=Vin×2 Iout=3.0V×80 mA=240 mw

Therefore, Eff=224/240=93.3% (Theoretical maximum).

[0121] The actual realized efficiency will be about 84% after accountingfor losses on the charge storage component 114 and the resistances ofthe switches 104, 106, 110, and 112.

[0122] This efficiency of the regulating charge pump 900 of FIG. 9 canbe compared to the case where a comparable array of green and white LEDsare driven directly from a battery with two linear current sourcecircuits where:

Pin=(VN^(IN)×2I_(OUT) _(—) _(WHT))+(V_(BAT)×I_(GREEN))=240+120=360 mW

Eff=224/360=62.2% (Theoretical Maximum)

[0123] The actual efficiency of the green driver is approximately80/120=66.7%.

[0124] The actual efficiency of a separate white LED driver is about0.9× calculated maximum:EffWht = 0.9 × (3.6 × 0.04/3.0 × 0.08)   = 0.9 × (0.144/0.240)   = 0.9(60%) ≈ 54%.

[0125] The overall combined efficiency of the two separate circuits isapproximately 62%. In addition, this alternative to the presentinvention requires two separate circuits, whereas the multiple outputregulated charge pump 900 of the embodiment in FIG. 9 offers improvedefficiency in a single circuit. Thus, the efficiency from a system pointof view is increased from approximately 62% to approximately 84% withthe embodiment of FIG. 9, and a saving of approximately 120 mW isobtained. In other words, the total power usage of the LEDs 150, 154drops from approximately 360 mW to approximately 240 mw. Thus, a savingsof 120/360=33.3% of total power of the LEDs is obtained. As previouslydiscussed, reduced power consumption and improved efficiency is highlydesirable in the art of battery-powered devices. The efficiency foralternative embodiments with different values of V_(IN) are set forth inthe following table.

Efficiency vs. Vin for a Single Multiple Output Regulated Charge Pump900 vs. Dual Single Output Charge Pumps with Linear Regulators

[0126] Two White LEDs at 20 mA each, Four Green LEDs at 10 mA eachEfficiency Efficiency System of single of Efficiency Efficiency ofoutput Green Of Single multiple White LED LED output pump + outputcharge linear linear regulated pump regulator regulator Charge Vin 103Pin Pout A B A + B Pump 100 3.2 V 256 mW wht + 144 mW wht + 50.6% 68.7%60.4% 81.5% 128 mW grn 88 mW grn — 3.6 V 288 mW wht + 144 mW wht +   45%  61% 53.7% 72.5% 144 mW grn 88 mW grn — 4.2 V 336 mW wht + 144 mW wht +38.5% 52.3%   46% 62.1% 168 mW grn 88 mW grn — 5.6 V 448 mW wht + 144 mWwht + 28.9% 39.2% 34.5% 46.6% 224 mW grn 88 mW grn —

[0127]FIG. 12 is a circuit diagram of an alternative embodiment of amultiple output regulating charge pump 1200 that includes compensationfor variations in a forward voltage drop V_(F) of a white LED 150. Theoverall functionality and operation of the regulating charge pump 1200is substantially similar to that of the regulating charge pump 900described above. Attention will be drawn to the differences between theregulating charge pumps 900 and 1200. The components comprising theregulating charge pump 1200 and the operation thereof can be assumed tobe otherwise substantially similar to that previously described withrespect to the regulating charge pump 900.

[0128] The regulating charge pump 1200 eliminates the resistor (R1) 132and the resistor (R2) 134. Instead, in the embodiment of FIG. 12, directconnection is made between the inverting input of the error amplifier124 and the node between the resistor (R3) 162 and a first white LED150.

[0129] The embodiment of FIG. 12 is advantageous because the sensesignal for the feedback circuit 140 (i.e., the voltage present at theinverting input of the error amplifier 124) is derived from the “output”of the white LED 150 comprising the first load 146. In contrast, in FIG.9, the sense signal is derived from the “input” of the white LED 150comprising the first load 146. The white LEDs 150 have the forwardvoltage drop V_(F) as is well known in the art. During use, the forwardvoltage drop V_(F) can change as the temperatures and currents of thewhite LEDs 150 change. Thus, the embodiment of FIG. 12 more closelytracks the actual operating condition of the white LEDs 150 than isobtained by tracking the first output voltage V_(OUT1) on the terminal142 directly.

[0130]FIG. 13 is a circuit diagram of a charge pump 1300 with loadcurrent regulation. The charge pump 1300 receives electrical power froma primary power source 102, and, in this embodiment, provides a firstregulated output V_(OUT1) on the terminal 142 and provides a secondregulated output V_(OUT2) on the terminal 144 in a manner that will bedescribed in greater detail below. The overall functionality andoperation of the regulating charge pump 1300 is substantially similar tothat of the regulating charge pump 1200 as previously described.Attention will be drawn to the differences between the regulating chargepumps 1200 and 1300 and the components comprising the regulating chargepump 1300. The operation thereof can be assumed to be otherwisesubstantially similar to that previously described with respect to theregulating charge pump 1200.

[0131] Like the charge pump 1200, the regulating charge pump 1300eliminates the current sensing resistor (R3) 162 and the current sensingresistor (R4) 164. Instead, in the embodiment of FIG. 13, an active loadcurrent regulator 163 replaces the current sensing resistors 162 and 164for more efficient operation. The active load current regulator 163causes a first sink current (ISINK1) 190 to flow through the first whiteLED 150 and causes a second sink current (ISINK2) 192 to flow throughthe second white LED 150.

[0132]FIG. 14 is a circuit diagram of the charge pump 1300 with loadcurrent regulation of FIG. 13 during a charge half-cycle, during whichthe charge pump 1300 provides power to a second load 152. In thisembodiment, V_(IN)=3.0 volts, and the arbitrary assumption is made thatthe switches 104 and 110 are closed. This places the charge storagecomponent C_(x) 114 in series with the power source 102, the variablecurrent source 122, and the second load 152. To maintain V_(OUT1) on theterminal 142 at 3.9 volts with V_(IN)=3.0 volts, a voltage ofapproximately 0.9 volts is required across the charge storage component114. The 2.1 volt difference between V_(IN) and the voltage across thecharge storage component 114 is thus available at the V_(OUT2) terminal144. A regulated direct current 156 will be provided by the power source102 to the charge storage component C_(x) 114 through the variablecurrent source 122 and to the second load 152 at 2.1V.

[0133] In the embodiment of FIGS. 13 and 14, each of the four green LEDs154 draws 15 mA of current, which results in a total regulated current156 of 60 mA. This current also causes voltage across the charge storagecomponent C_(x) 114 to increase by approximately 0.9V. The outputvoltage available at the V_(OUT2) terminal 144 is approximately 2.1 Vand is within the optimal range to power the green LEDs 154.

[0134]FIG. 15 is a circuit diagram of the charge pump 1300 with loadcurrent regulation of FIG. 13 during a discharge half-cycle during whichregulated voltage and current are provided to multiple branches of afirst load 146. The charge storage component C_(x) 114 is connected inseries with the power source 102 and the first load 146 via the closedswitch switches 106 and 112. In this condition, the power source 102provides current through the charge storage component 114, which adds0.9 volts to V_(IN). The total voltage is applied to the first load 146via the terminal 142. In this embodiment, each white LED 150 draws 30 mAof current for a total regulated current 156 of 60 mA.

[0135] The embodiment of the multiple output regulated charge pump 1300described herein is particularly advantageous in that the currentsrequired for operation of the first load 146 and the second load 152 aresubstantially identical. Also, in the application of cell phones, PDAs,and the like, both the white LEDs 150 of the first load 146 and thegreen LEDs 154 of the second load 152 are normally on at the same time.The 10 μF capacitive element connected in parallel with the two whiteLEDs 150 filters the current in the first load 146 such that the ISINK1current 190 and the ISINK2 current 192 are substantially continuous. Inalternative embodiments, the 10 μF capacitive element can be eliminatedto allow the ISINK1 current 190 and the ISINK2 current 192 to pulse at50% duty cycle and double amplitude; however, the light output of theseembodiments will be less than the embodiment described above.

[0136] The overall system level efficiency, defined here as the powerdissipated in the LEDs 150, 154 neglecting switch loses at the minimumV_(IN) of 3.0 volts provided by the power source 102 is defined by:

Eff=Pout/Pin=(Pwhite+Pgreen)/Pin

Pout=3.6V×60 mA+2.0V×60 mA=336 mw

Pin=Vin×2×Iout=3.0 volts×120 mA=360 mw

Therefore, Eff=336/360=93.3% (Theoretical maximum).

[0137] The actual realized efficiency will be about 84% after accountingfor losses on the charge storage component 114 and the resistance of theswitches 104, 106, 110, and 112.

[0138] This efficiency of the regulating charge pump 1300 of FIG. 13 canbe compared to the case where a comparable array of green and white LEDsare driven directly from a battery with two linear current sourcecircuits where:

Pin=(VN×2×I_(OUT) _(—) _(WHT))+(V_(BAT)×I_(OUT) _(—) _(GRN))=360+180=540mw

Eff=336/540=62.2% (Theoretical Maximum)

[0139] The actual efficiency of the green driver is 120/180=66.7%.

[0140] The actual efficiency of a separate white LED driver is about0.9× calculated maximum:Eff_(WHT) = 0.9 × (3.6 × 0.06/3.0 × 0.12)   = 0.9(0.216/0.360)     = 0.9 × (60%) ≈ 54%

[0141] The overall combined efficiency of the two separate circuits isapproximately 62%. In addition, this alternative to the presentinvention requires two separate circuits, whereas the multiple outputregulated charge pump 1300 of this embodiment offers improved efficiencyin a single circuit. Thus, the efficiency from a system point of view isincreased from approximately 62% to approximately 84% with theembodiment of FIG. 13. A saving of approximately 180 mW is obtained. Inother words, the total power usage of the LEDs 150, 154 drops fromapproximately 540 mW to approximately 360 mw. Thus, a savings of180/540=33.3% of total power of the LEDs 150, 154 is obtained. Aspreviously discussed, reduced power consumption and improved efficiencyare highly desirable in the art. The efficiency for alternativeembodiments with different values of V_(IN) 103 are given in thefollowing table.

Efficiency vs. Vin for a Single Multiple Output Regulated Charge Pump1300 vs. Dual Single Output Charge Pumps with Linear Regulators

[0142] Two White LEDs at 30 mA each, Four Green LEDs at 15 mA eachEfficiency Efficiency System of single of Efficiency Efficiency ofoutput Green Of Single multiple White LED LED output pump + outputcharge linear linear regulated pump regulator regulator Charge Vin 103Pin Pout A B A + B Pump 100 3.2 V 384 mW wht + 216 mW wht + 50.6% 68.7%60.4% 81.5% 192 mW grn 132 mW grn — 3.6 V 432 mW wht + 216 mW wht +  45%   61% 53.7% 72.5% 216 mW grn 132 mW grn — 4.2 V 504 mW wht + 216mW wht + 38.5% 52.3%   46% 62.1% 252 mW grn 132 mW grn — 5.6 V 672 mWwht + 216 mW wht + 28.9% 39.2% 34.5% 46.6% 336 mW grn 132 mW grn —

[0143] The output voltage V_(OUT1) on the terminal 142 will typically be3.9 volts, but can increase or decrease as the forward voltage of thewhite LED 150 changes. This is important, because the regulating chargepump 1300 of the embodiment of FIG. 13 uses minimum output power at alltimes. The forward ISINK1 current 190 and the forward ISINK2 current 192of the white LEDs 150 can easily be reduced by reducing the 150 mVreference voltage 206 on the OpAmp 194 of the load current regulator 163to provide a dimming feature. When the ISINK1 current 190 and the ISINK2current 192 decrease, the forward voltage drop V_(F) decreases. In thecircuit of FIG. 13, the output voltage V_(OUT1) on the terminal 142follows to provide the highest possible efficiency. Temperature effectson the forward voltage V_(F) are also automatically compensated.

[0144] The total current through the four green LEDs 154 will beidentical to the white LED 150 total current (60 mA), since inequilibrium, the C_(x) charge current is equal to the discharge current.In the circuit of FIG. 13, the green LED 154 current will flow onlyduring the charge half cycle. If a filter capacitor is added on theV_(OUT2) terminal 144 in parallel to ground, DC current will flow in thegreen LEDs 154 in a similar manner to that previously described withrespect to the white LEDs 150. Current sharing in the green LEDs 154 isof less concern than the white LEDs 150, since the green LEDs aregenerally used only to provide back light for the cell phones keys. Thewhite LEDs 150 are used to backlight the color TFT display, and shouldhave equal currents to prevent uneven lighting and uneven coloration ofthe display.

[0145] The circuit of FIG. 13 operates at various frequencies and valuesof the charge storage component 114. In general, the charge storagecomponent 114 should have a high value, and the frequency of the squarewave oscillator 120 should be as high as possible to keep the ripplevoltage on the charge storage component 114 low. This will minimizelosses in the charge storage component 114 and will extend the dynamicrange of the output voltage V_(OUT1) on the terminal 142 and the outputvoltage V_(OUT2) on the terminal 144 because the charge storagecomponent 114 ripple voltage will not limit the extremes of the inputvoltage V_(IN) on the input terminal 103, the output voltage V_(OUT1) onthe terminal 142 and the output voltage V_(OUT2) on the terminal 144. Itshould also be appreciated that the present invention is scalable toother quantities of LEDs 150, 154 by adding or removing the N-FETs 196,200 to the current mirror in the load current regulator 163, describedbelow.

[0146]FIG. 16 is a detailed circuit diagram of the charge pump 1300 withload current regulation of FIG. 13. FIG. 16 illustrates one embodimentof the switches 104, 106, 110, 112 in greater detail. Each of theswitches 104 and S2 106 comprises a type 74ACT11240 inverter and a typeNDS332P P-FET. The input of the inverter in the switch 104 receives theT1 control signal 172, and the input of the inverter in the switch 106receives the T2 control signal 174. The output of the inverter in eachswitch 104, 106 is connected to the gate of the associated P-FET.

[0147] The switch 110 comprises a type 74ACT11240 inverter with theoutput thereof connected to the gate of a type NDS332P P-FET. The switch110 also comprises two type 74ACT11240 inverters connected in serieswith the output of the second inverter connected to the gate of a typeFDV303N N-FET. The type NDS332P P-FET and the type FDV303N N-FET areconnected as a parallel pair so that the first terminal of the switch110 floats above the circuit ground 130 without turning off the switch110. The inputs of the switch 110, corresponding to the inputs of theinverters, receives the T1 control signal 172.

[0148] The switch 112 comprises two type 74ACT11240 inverters eachhaving the output thereof connected to the gate of a respective typeNDS332P P-FET. The input of each of the inverters of the switch 112receives the T2 control signal 174. The two type NDS332P P-FETs areconnected in series to form the two terminals of the switch 112, whereina first terminal of the switch 112 is connected to the second terminalof the switch 104. The second terminal of the switch 112 is connected tothe terminal 142 to provide the output voltage V_(OUT1). The firstterminal of the switch 110 is connected to the second terminal of theswitch 106. The second terminal of the switch 110 is connected to theterminal 144 to provide the output voltage V_(OUT2).

[0149] The variable current source 122 of the embodiment of FIG. 16comprises two type LM6152 OpAmps (U1B and U1A), two type NDS332P P-FETs(Q1 and Q3), a type 74ACT11240 inverter, and a type 2N3904 transistor(Q2). The output of a first OpAmp (U1B) is connected to the base of thetransistor (Q2). The variable current source 122 also comprises a 20 nFcapacitor (C1) connected between the output and the inverting input ofthe first OpAmp (U1B) and between the base and emitter of the transistor(Q2). A 400 Ω resistor (R2) is connected between the emitter of thetransistor (Q2) and the circuit ground 130.

[0150] The input of the inverter receives the T1 control signal 172, andthe output of the inverter is connected to the gate of a first typeNDS332P P-FET (Q1). The inverter and the first type NDS332P P-FET (Q1)interrupt the charge current to the charge storage component 114 whenthe charge storage component 114 is discharging into the first load 146.The drain of the first type NDS332P P-FET (Q1) is connected to thecollector of the transistor (Q2), and the source of the first typeNDS332P P-FET (Q1) is connected to the non-inverting input of the secondOpAmp (U1A). A 200-ohm resistor (R1) is connected between thenon-inverting input of the second OpAmp (U1A) and the input terminal103. A 2-ohm resistor (R4) is connected between the input terminal 103and the inverting input of the second OpAmp (U1A). The output of thesecond OpAmp (U1A) is connected to the gate of the second type NDS332PP-FET (Q3). The source of the second type NDS332P P-FET (Q3) isconnected to the inverting input of the second OpAmp (U1A), and to thedrain of the second type NDS332P P-FET (Q3) is connected to the firstterminal of the switch 104. A resistor (R3) 184 is connected between theinput terminal 103 and the first terminal of the switch 106.

[0151] Note that in FIG. 16, the variable current source 122 is locatedin the path between the input voltage terminal 103 and the switch 104rather than being in the path between the switch 110 and the outputterminal 144, as described in FIGS. 4, 9, 12 and 13. It should beunderstand that the variable current source 122 in FIG. 16 is in thecharging path of the charging component 114 and controls the chargingcurrent in the same manner as described above in connection with FIGS.4, 9, 12 and 13.

[0152] As discussed above, the regulating charge pump 1300 of FIG. 16also comprises an error amplifier 124. The output of the amplifier 124is connected to inverting input of the first OpAmp (U1B) of the variablecurrent source 122 to regulate the current supplied by the variablecurrent source 122. In this embodiment, the amplifier 124 is a LM6152type operational amplifier (OpAmp). The inverting input of the amplifier124 is connected to the output terminal of one of the white LEDs 150.This enables the regulating charge pump 1300 of this embodiment to trackchanges in the forward voltage of the white LED 150. A voltage reference126 is connected to the non-inverting input of the amplifier 124. Inthis embodiment, the voltage reference 126 provides a fixed, 300 mVsignal. In alternative embodiments, the voltage reference 126 provides avariable signal. In further alternatives, the voltage reference 126 isselectable among a plurality of fixed values.

[0153] In the embodiment of FIG. 16, the output voltage V_(OUT1) on theterminal 142 is regulated at approximately 3.9 volts, which correspondsto a voltage at the output terminal of one of the white LEDs 150 of 300mV with a 3.6-volt forward voltage drop. The output voltage V_(OUT1) onthe terminal 142 is provided to the first load 146. In the embodiment ofFIG. 16, the first load 146 comprises a capacitive component ofapproximately 10 μF in parallel with a plurality of white LEDs 150.

[0154] The regulating charge pump 1300 also provides a second outputvoltage V_(OUT2) on the terminal 144 to the second load 152. In thisembodiment, the output voltage V_(OUT2) on the terminal 144 is regulatedto provide approximately 40 mA of current to the second load 152. Inthis embodiment, the output voltage V_(OUT2) on the terminal 144 is thevoltage present at the second terminal of the switch 110, and the secondload 152 comprises a plurality of green LEDs 154 connected in parallelbetween the V_(OUT2) terminal 144 and the circuit ground 130.

[0155] In the embodiment of FIG. 16, the second load 152 is interposedbetween the variable current source 122 and circuit ground 130. In thisembodiment, the regulated current 156 flowing from the variable currentsource 122 is available to the second load 152 at the difference betweenthe voltage developed by the power source 102 and the steady statecharge on the charge storage component 114 minus losses in the switches104, 110.

[0156] The regulating charge pump 1300 of this embodiment also comprisesa load current regulator 163. The load current regulator 163 regulatesthe ISINK1 current 190 through a first white LED 150 of the first load146 and the ISINK2 current 192 through the second white LED 150 of thefirst load 146. In this embodiment, the ISINK1 current 190 and theISINK2 current 192 are regulated at 30 mA each to provide improvedparity of lighting from the two white LEDs 150.

[0157] The load current regulator 163 of this embodiment comprises atype LM6152 OpAmp 194, two type FDV303N N-FETs 196, 200, two 5-ohmresistors 202, 204, and a voltage reference (V_(REF2)) 206. In thisembodiment, the V_(REF2) voltage reference 206 provides a fixed 150 mVsignal to the inverting input of the OpAmp 194. The non-inverting inputof the OpAmp 194 is connected to a first terminal of the resistor (R10)202, and the output of the OpAmp 194 is connected to the gates of theN-FETs 196, 200. Respective first terminals of the resistors 202 and 204are connected to the sources of the N-FETs 196, 200, respectively. Thesecond terminals of the resistors 202, 204 are connected to the circuitground 130. The N-FETs 196, 200 operate as a current mirror so that theISINK2 current tracks the ISINK1 current, which controls the OpAmp 194.In the embodiment of FIG. 16, the voltage reference (V_(REF)) 126 in theerror amplifier 124 is selected to provide a sufficient voltage acrossthe N-FET 196 and the resistor 202 to ensure linear operation.

[0158] When the ISINK1 current 190 and the ISINK2 current 192 havemagnitudes of 30 mA, the voltage appearing at the non-inverting input ofthe OpAmp 194 of the load current regulator 163 will be approximately150 mV, and the voltage appearing at the drain of the N-FET 196 will beapproximately 300 mV. Thus, the error amplifier 124 will generate aminimal corrective signal to the variable current source.

[0159] In particularly preferred embodiments, the regulating chargepumps 100, 200, 900, 1300 are fabricated on respective singlesemiconductor chips in a manner well understood by one of skill in theart. However, it will also be appreciated that the regulating chargepump 100, 200, 900, 1300 described herein can also be fabricated fromdiscrete components and with circuit elements of different parameters toprovide different operating parameters and to accommodate loads 152, 400and power supplies 102 having different parameters. It will be furtherappreciated that additional switches and charge storage components canbe included with modifications to the switch timing control to enablealternative boost multiplications in alternative embodiments of theinvention.

[0160] Although the foregoing description of the preferred embodiment ofthe present invention has shown, described, and pointed out thefundamental novel features of the invention, it will be understood thatvarious omissions, substitutions, and changes in the form of the detailof the apparatus as illustrated as well as the uses thereof, may be madeby those skilled in the art without departing from the spirit of thepresent invention. Consequently, the scope of the present inventionshould not be limited to the foregoing discussions, but should bedefined by the appended claims.

What is claimed is:
 1. A charge pump configured to provide two outputvoltages by alternately charging and discharging a charge storagecomponent, wherein the charge storage component is coupled in serieswith a supply voltage and a first load to discharge the charge storagecomponent and to provide power to the first load, and wherein the chargestorage component is coupled in series with the supply voltage and asecond load to charge the charge storage component and to provide powerto the second load.
 2. The charge pump of claim 1, wherein a firstvoltage provided to the first load is different from a second voltageprovided to the second load.
 3. The charge pump of claim 2, wherein thefirst voltage ranges from 3.0 volts to 5.6 volts, and wherein the secondvoltage ranges from 1.5 volts to 2.5 volts.
 4. The charge pump of claim1, wherein a first voltage is provided to the first load and a secondvoltage is provided to the second load, and wherein at least one of thefirst voltage and the second voltage is regulated at a voltage differentthan the supply voltage.
 5. The charge pump of claim 1, wherein a firstvoltage is provided to the first load and a second voltage is providedto the second load, and wherein the first voltage and the second voltageare regulated independently of the supply voltage.
 6. The charge pump ofclaim 1, wherein a first current provided to the first load and a secondcurrent provided to the second load are substantially equal.
 7. Thecharge pump of claim 6, wherein the charge pump regulates at least oneof the first current and the second current.
 8. The charge pump of claim7, wherein the first load comprises at least one light emitting diode,and wherein the second load comprises at least one light emitting diode.9. The charge pump of claim 7, further comprising a variable currentsource coupled between the charge storage component and the second loadduring the charging of the charge storage component to regulate thesecond current.
 10. The charge pump of claim 7, wherein the first loadcomprises a plurality of white light emitting diodes for lighting acolor display, and wherein the second load comprises a plurality ofgreen light emitting diodes for lighting a key pad.
 11. A charge pumpregulator configured to drive at least two independent loads, the chargepump regulator comprising: a charge storage device; and a plurality ofswitches that alternately couple the charge storage device in serieswith a supply voltage to a first load and to a second load, wherein thecharge storage device charges when the charge storage device is coupledto the second load and discharges when the charge storage device iscoupled to the first load.
 12. The charge pump regulator of claim 11,further comprising a switch timing control that operates the pluralityof switches so as to inhibit having the charge storage device coupled inseries with the supply voltage and both the first and second loadssimultaneously.
 13. The charge pump regulator of claim 11, furthercomprising a feedback circuit that regulates the charging of the chargestorage device based on an output voltage across the first load.
 14. Thecharge pump regulator of claim 13, wherein the feedback circuitcomprises a variable current source coupled in series with the secondload and an error amplifier configured to control the variable currentsource based on a difference between a feedback voltage indicative ofthe output voltage across the first load and a reference voltage. 15.The charge pump regulator of claim 14, wherein the reference voltage isselectable among a plurality of reference voltage values.
 16. The chargepump regulator of claim 11, further comprising a feedback circuit thatregulates the charging of the charge storage device based on currentprovided to the first load.
 17. The charge pump regulator of claim 11,wherein the charge storage device is a non-polarized capacitor.